The apparatus disclosed herein, in general, relates to electrical enclosures. More particularly, the apparatus disclosed herein relates to electrical enclosures that provide front access to electrical bus members, multiple electrical components, and apparatuses housed within the electrical enclosures. Furthermore, the apparatus disclosed herein relates to electrical bus assemblies for electrical enclosures and arc resistant electrical enclosures.
Medium voltage electrical components and apparatuses, for example, circuit breakers, potential transformers, current transformers, control power transformers, etc., are often housed in an electrical enclosure called a switchgear cabinet. The medium voltage electrical components and apparatuses operate, for example, in a range of about 1000 volts to about 100,000 volts. The switchgear cabinet for medium voltage equipment typically occupies a large space and is difficult to access. As such, maintenance and space considerations are driving factors in the design of new electrical equipment. There is a need for constructing a switchgear assembly that makes efficient use of the available floor space and minimizes the time required for inspection, repair and maintenance of equipment accommodated within the switchgear assembly.
Furthermore, a certain amount of space is required between adjacent equipment and structures such as walls and the switchgear cabinet per the national electric code (NEC) and other local codes. An entire room is typically allocated for a medium voltage switchgear cabinet. Space is a critical factor in industrial applications, data center facilities and marine equipment, where space is limited. Allocation of a substantial amount of space, for example, an entire room for the medium voltage switchgear cabinet is an undesirable and inefficient use of valuable floor space.
Switchgear cabinets, particularly medium voltage metal clad switchgear cabinets are often damaged due to arcing. An explosion caused by arcing within a switchgear cabinet results in significant economic loss due to interruption of energy distribution, and damage of the switchgear cabinet and the components or equipment accommodated in the switchgear cabinet. Consequently, maintenance personnel inspecting and servicing the switchgear cabinets have to wear protective gear that is bulky and expensive. Typical arc resistant switchgear cabinets tend to be very large, for example, cabinets are 36 inches wide and 90 inches deep and often have heavy sheet metal enclosures. Such configurations require significant space. Some switchgear cabinets employ an external arcing chamber that limits the configuration of components, equipment, etc., within the switchgear cabinet.
Conventional switchgear cabinets available in markets, for example, in Europe and Asia are built in accordance with the International Electrotechnical Commission (IEC) standards. However, these switchgear cabinets have cable connection bus bars in the rear making it difficult to install and service electrical components and the bus bars accommodated within these switchgear cabinets. Furthermore, conventional switchgear cabinets utilize bar type current transformers that are mounted in the rear making it difficult to replace a transformer in the field if one of the transformers fail. Consequently, there is a need for positioning cable connection bus bars at the front of a switchgear cabinet for both safety and accessibility. Furthermore, there is a need for mounting transformers in the front of the switchgear cabinet for easier accessibility for maintenance and inspection.
Moreover, there are significant limitations with respect to the size of potential transformers and control power transformers that are available in conventional switchgear cabinets. For example, the maximum voltage for a potential transformer in a conventional metal clad switchgear cabinet is about 5000V and the maximum power for a control power transformer is about 5 kVA.
Conventional metal clad switchgear cabinets for the North American market need to meet stringent Institute of Electrical and Electronics Engineers (IEEE) requirements and American National Standards Institute (ANSI) requirements. These standards require a circuit breaker to be tested inside the switchgear cabinets that have limited cooling and therefore limiting the temperature rise within the switchgear cabinet becomes a major challenge. Furthermore, as per International Electrotechnical Commission (IEC) standards, barriers between compartments in the switchgear cabinets are not a requirement, therefore cooling the circuit breaker within the switchgear cabinet is much easier. IEC designed equipment, would have to be derated significantly if no changes are made.
Furthermore, conventional metal clad switchgear cabinets pose additional challenges to meet ANSI and Underwriters Laboratories (UL) requirements because of limited space and limited cooling. In addition, IEEE/ANSI designed equipment requires bus bars within the switchgear cabinet to be insulated, making it more difficult to cool the critical current carrying bus bars in certain compartments of the switchgear cabinet that accommodate the circuit breaker. Alternatively, expensive heat sinks have to be employed to limit temperature rise. The addition of heat sinks is a difficult task in the compact space available and poses significant challenges to pass the required lightning impulse test due to space limitations and the shape of the heat sink.
Hence, there is a long felt but unresolved need for an arc resistant front accessible metal clad switchgear assembly that has a compact footprint and provides front access to electrical components and equipment accommodated in the switchgear assembly for inspection, testing and maintenance with limited space requirements and without protective gear. Furthermore, there is a need for a compact front accessible switchgear assembly that allows successful testing of the electrical components, for example, circuit breakers that are accommodated in the switchgear assembly without additional heat sinks.